The present disclosure relates to a method for register correction in a web processing machine having a delay section.
Although reference is primarily made below to web-fed rotary printing presses of central cylinder design, the disclosure is not restricted thereto but instead is aimed at all types of processing machines in which a product web or material web runs through a delay section. A delay section in the sense of the disclosure is a section in the machine which forwards an incoming web tension change only with a time delay. The incoming web tension is not changed but substantially transported through unchanged, so that the web tension after the running time (therefore with the time delay) appears after the delay section. A delay section is formed, for example, when the product web wraps around one or more rolls, such as central cylinders, cooling or drying rolls, the web draw approximately not changing as a result of the web clinging to the roll during the roll contact. The time delay is also designated dead time.
Web-fed rotary printing presses of central cylinder design are particularly widespread in the area of flexographic printing but are also known, for example, in offset printing or digital printing. The central cylinder is also designated a common impression (CI) cylinder.
The central cylinder design is distinguished by the fact that the product web wraps around the central cylinder, the tensile force in the product web (web draw) approximately not changing as a result of the web clinging to the cylinder during the contact. As a result, known decoupling strategies which counteract the automatic production of a longitudinal register error or color register error (deviation of the actual position of the product (e.g. color separation) from the intended position) as a result of another actuating action (e.g. a longitudinal register correction or web draw correction) by means of specifically driving the processing device producing the relevant product cannot be applied. (A register error arises in web processing machines as a result of an actuating action when the actuating action leads to a change in the web tension. This is because the web tension change is then propagated through the machine and in the process leads to register errors.)
It is therefore desirable, even for these cases, to have a possible way of avoiding longitudinal register errors as a result of actuating movements or at least to keep the said errors small.